Building control systems control various aspects of a building, including comfort, safety, lighting and other aspects. With respect to comfort, one aspect of a building control system includes heating, ventilation and air conditioning (HVAC). An HVAC system involves conditioning of the air within an area, zone or room. Such conditioning includes providing heated air, cooled air, fresh air, circulated air and/or the like to the particular area depending on various factors. The HVAC system includes a system of ducts that terminate in particular areas or zones. The termination points are controlled by ventilation dampers or damper systems. Each ventilation damper/damper system is operative to control the flow of air from the respective termination point.
Ventilation dampers/damper systems are thus one component of a building control system that are used to help with the aspect of comfort and safety. In summation, ventilation dampers/dampers systems (collectively, dampers) are used for temperature control, pressure regulation, air circulation and/or replacement of stale air.
Basic dampers are positionable into either a fully opened or a fully closed position. This provides only either full air flow or no air flow. It is better, however, to use intermediate levels of openness in addition to the fully opened and fully closed positions in order to better control ventilation. For example, in order to maintain a particular temperature, the damper may be opened to allow the flow of conditioned air into the room. If only two states (open and closed) are allowed, the system will constantly be cycling on and off to maintain the particular temperature. With intermediate levels of openness, an amount of conditioned air may be gradually modulated into the room/zone until a quasi-steady state level is achieved (in other words, the flow of conditioned air through the damper more or less equals the thermal load variables within the room that are changing the controlled air requirements of the room).
Modulating control dampers achieve this elevated level of control over damper position and thus provide better control over temperature, pressure regulation and/or air replacement. Modulating control dampers include a modulating control. The modulating control typically receives signals representative of a particular position (percentage open) and then control an actuator to achieve that position in accordance with particular parameters. A modulating control actuator is used to control position of the damper and thus control air flow. The modulating control utilizes digital and/or analog circuits that operate a motor to cause the damper to travel to and stop in the position identified by the received controls.
It has been recognized that the needs of the ventilation system change in the presence of fire and its attendant smoke. In certain situations, it is advantageous to vent heat away from affected areas unless smoke is present, in which case the area should be sealed. Ventilation dampers may be configured to perform such functions during a fire and smoke event.
Dampers having modulating control typically cannot be used for fire and smoke events because the circuits that control position of the motor are not resilient enough to tolerate the extensive heat that accompanies such fire and smoke events. Indeed, standards define the conditions under which the above described fire and smoke operation must be able to be carried out. The types of digital and analog circuitry that currently perform modulating control may not meet those standards.
Accordingly, the prior art has employed separate dampers in the ducts of buildings, i.e. one damper for comfort control and one damper for fire and smoke control. The comfort control damper may employ a modulating actuator control that opens the damper to a select position of large number of positions. The fire and smoke control damper employs a simpler two-state actuator control that is either open or closed. With this system, the comfort control damper and actuator need not operate fully or function in any manner during a fire and smoke event, and may thus employ significant position control circuitry. Meanwhile, the fire control damper requires fewer control elements, and thus can readily be made to withstand the higher temperature operating requirements.
One problem with the above-described arrangement for providing dampers in a building control system is the cost associated with requiring multiple dampers for multiple functions for the same room or space. There is a need, therefore, for a system that overcomes the shortcomings of the prior art ventilation damper arrangements.